Hub motors are commonly found on electric bicycles, which are motors designed to be incorporate into a hub of a wheel for driving it to rotate directly. However, as each spoke in a bicycle rim is fixed to the hub, the installation of hub motor can be very time consuming. In addition, since rims from different bicycle manufacturers are produced with different specifications that are not standardized, all those rims may have to be redesigned for allowing the electric hub motor to be installed therein. Therefore, it is required to have an axial-flux disc motor that can be adapted for rims of different bicycle manufacturers as it can be attached and mounted to a side of any bicycle.
Moreover, most conventional disc motors are designed specifically for electronic products that can be activated with comparatively small power, so that while applying such conventional disc motors for driving vehicles such as bicycles, a serious shortage of torque outputted from such low-current disc motors may occur. On the other hand, although the conventional axial-flux motors for automotive applications are able to produce sufficient torque for driving vehicles, they are generally very bulky and built with thick and heavy structure due to their mechanical design. Thus, it is required to have a thin and light-weighted axial-flux disc motor capable of producing sufficient torque for automotive applications.
There are already many studies for overcoming the aforesaid shortcomings. One of which is an ultra-thin motor, disclosed in TW Pat. No. I303122, by that not only the assembly and mass production efficiencies of the motor are improved, but also the problem troubling the thinning of conventional radial air-gap motors, such as the stacking of magnetic materials, is resolved.
The second such study relates to an ultra-thin spindle motor with low run-out, disclosed in TW Pat. No. I260595, in that with the innovated internal mechanism designed inside the spindle motor, the problems troubling the conventional motors are improved in terms of operational smoothness and reduced thickness.
The third such study relates to an axial-flux motor for ceiling fans that is disclosed in TW Pat. No. M361170. Comparing with the conventional radial motors, not only the aforesaid motor is less complicated in structure and is capable of operating at a higher efficiency, but also it can be built thinner than those conventional radial motors while preserving a large effective flux area and thus operating at a higher driving efficiency. However, it may not be suitable for automotive applications as it is intended in the present disclosure.
The fourth such study relates to a heat sink of a motor configured with ribs, disclosed in TW Pat. No. I318036, in which heat emitting from heat-generating components of a high-power motor is transmitted from their corresponding fixtures to the motor base, ribs and frame of the motor and thus is dissipated. The ribs built inside the motor are acting not only for heat dissipation, but also for fixedly securing the internal components of the motor. However, the construction of the ribs is neither aiming for building a thinner motor, nor for reinforcing the structure integrity of the motor.
The fifth such study relates to a cooling device for external rotor motors, disclosed in TW Pat. No. 52985, in which there are ribs mounted on the rotors to be used for causing airflows during the operation of the motor, and the airflows that are flowing inside the flow channels designed inside the motor for heat dissipation will enable temperatures of the components inside the stators to be distributed evenly. However, the construction of the ribs is neither aiming for building a thinner motor, nor for reinforcing the structure integrity of the motor.
The sixth such study relates to an axial gap motor including a rotor and two stators, disclosed in U.S. Pat. No. 7,679,260 B2, in which the rotor has a rotor frame that is configure with a plurality of ribs to be used for improving the rigidity of the rotor, fixing the magnets of the rotor, and the suppression of the vibration and noise of the motor that are generated when the motor is in operation. However, the construction of the ribs is neither aiming for building a thinner motor.
The seventh such study relates to an axial gap electric motor having two stators, two rotors and two output shafts, disclosed in U.S. Pat. No. 7,256,524 B2. According to this configuration, the motor is cooled by a water jacket that is provided for cooling water to flow therethrough, and the two output shafts are capable of rotating independently at different rotation speeds. However, the aforesaid motor may not be suitable for automotive applications.
The eighth such study relates to a synchronous axial field electrical machine, disclosed in U.S. Pat. No. 7,170,212 B2. According to this configuration, the axial field electrical machine is basically a three-phase motor constructed with two rotors, one stator and two annular arrays of flat coils, i.e. a first annular array of flat coils and a second annular array of flat coils, that are arranged respectively on two different layers of the axial field electrical machine while enabling the coils of the second array to offset in a circumferential direction relative to the coils of the first array. However, the aforesaid synchronous axial field electrical machine is constructed neither aiming for building a thinner motor, nor for reinforcing the structure integrity of the motor.
Nevertheless, with reference to all the aforesaid patents, the currently available disc motors are designed specifically for electronic devices that are all small power motor since the coils capable of being embedded therein are micro/nano scaled that they can not sustain the current loads of other common-sized motors, not to mention that the torques that they can provided are limited and thus are not sufficient for any automotive applications. On the other hand, for those other conventional motors that can produce sufficient torque for driving a vehicle, they are generally very bulky and built with thick and heavy structure due to their mechanical design. Thus, it is required to have a thin and light-weighted axial-flux disc motor capable of producing sufficient torque for automotive applications.
Conventionally, the axial-flux motor is used in low-power, low-torque and high-speed applications, such as the electrical rotary motors in 3C electronic products including optical drivers and hard drives. Please refer to FIG. 1, which is a schematic diagram showing a conventional motor for optical drive. As shown in FIG. 1, the motor is comprised of: a back iron 11, a coil 12, an axis 13, a bearing 14 and a yoke 15. As the motor is a coreless structure whose coil 12 is winding on the back iron 11, the power and the torque produced thereby are comparatively smaller so that the motor can only be adapted for limited application. Please refer to FIG. 2, which is a schematic diagram showing a conventional disc motor. As shown in FIG. 2, the motor comprises: a stator frame 21, a motor 22, a coil 23, a bearing 24, a rotor frame 25, a bearing 26, a rotor 27, a fixing screw 28 and a permanent magnet 29. As the axial-flux disc motor of FIG. 2 can achieve a larger effective flux area, it can produce high power and high torque outputs. Nevertheless, owing to the generation of such high power and high torque outputs, huge normal force will be generated during the operation of the motor, that can achieve 3000 newtons (N) to 4000 newtons (N). Due to the structural deficiency of the disc motor and the generation of the huge normal force, the disc motor can easily be deformed which may cause the air gap inside the motor to deform accordingly for adversely affecting the operation smoothness of the motor, or even damaging the same.
Therefore, it is in need of a disc motor adapted for high-power and high-torque applications that is capable of achieving a torque density that is larger than 6 Nm/kg without causing any structural deformation to its thinness while outputting a large torque.